The C-H... O Hydrogen Bond in Crystals

OVER the past ten years, numerous examples of `short' intermolecular distances between a carbon atom with at least one hydrogen atom attached to it and an oxygen atom have appeared in papers on the crystal structures of organic molecules. By `short' it is meant that the intermolecular distance is considerably less than the sum of the van der Waals radii for the atoms or groups concerned. In practically all cases, the significance of these interactions has not been noted.